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<FONT color="green">001</FONT>    package gates;<a name="line.1"></a>
<FONT color="green">002</FONT>    <a name="line.2"></a>
<FONT color="green">003</FONT>    import register.Register;<a name="line.3"></a>
<FONT color="green">004</FONT>    import gates.MatrixGate;<a name="line.4"></a>
<FONT color="green">005</FONT>    import mathtools.*;<a name="line.5"></a>
<FONT color="green">006</FONT>    <a name="line.6"></a>
<FONT color="green">007</FONT>    /**Matrix representation of a Z pauli gate.<a name="line.7"></a>
<FONT color="green">008</FONT>     * This implements Gate interface, so consult this for public methods.<a name="line.8"></a>
<FONT color="green">009</FONT>     * The constructor for this gate is protected, so generating such an object is left<a name="line.9"></a>
<FONT color="green">010</FONT>     * for the factory class &lt;code&gt;Factory&lt;/code&gt;<a name="line.10"></a>
<FONT color="green">011</FONT>     * @author Jan Zaucha<a name="line.11"></a>
<FONT color="green">012</FONT>     * <a name="line.12"></a>
<FONT color="green">013</FONT>     */<a name="line.13"></a>
<FONT color="green">014</FONT>    public class ZMatrix extends MatrixGate{<a name="line.14"></a>
<FONT color="green">015</FONT>    <a name="line.15"></a>
<FONT color="green">016</FONT>            /**target bit*/<a name="line.16"></a>
<FONT color="green">017</FONT>            private int target;<a name="line.17"></a>
<FONT color="green">018</FONT>            /**Z matrix*/<a name="line.18"></a>
<FONT color="green">019</FONT>            private Matrix Z;<a name="line.19"></a>
<FONT color="green">020</FONT>            <a name="line.20"></a>
<FONT color="green">021</FONT>            /**<a name="line.21"></a>
<FONT color="green">022</FONT>             * Protected constructor for a matrix representation of a Z pauli gate<a name="line.22"></a>
<FONT color="green">023</FONT>             * Requires a target bit for the gate to operate on, however if the target bit is<a name="line.23"></a>
<FONT color="green">024</FONT>             * -1 the gate will be applied to all qubits<a name="line.24"></a>
<FONT color="green">025</FONT>             * @param target the target bit for phase shift (counting qubits from 0)<a name="line.25"></a>
<FONT color="green">026</FONT>             */<a name="line.26"></a>
<FONT color="green">027</FONT>            protected ZMatrix (int target){<a name="line.27"></a>
<FONT color="green">028</FONT>                    this.target=target;<a name="line.28"></a>
<FONT color="green">029</FONT>                    Z = new Matrix(2,2,0);<a name="line.29"></a>
<FONT color="green">030</FONT>                    Z.setElement(0,0,new Complex(1));<a name="line.30"></a>
<FONT color="green">031</FONT>                    Z.setElement(1, 1,new Complex(-1) );<a name="line.31"></a>
<FONT color="green">032</FONT>            }<a name="line.32"></a>
<FONT color="green">033</FONT>            <a name="line.33"></a>
<FONT color="green">034</FONT>            <a name="line.34"></a>
<FONT color="green">035</FONT>            /**Applies the Z gate to register r.<a name="line.35"></a>
<FONT color="green">036</FONT>             * <a name="line.36"></a>
<FONT color="green">037</FONT>             * @param r - Register to apply gate to.<a name="line.37"></a>
<FONT color="green">038</FONT>             */<a name="line.38"></a>
<FONT color="green">039</FONT>            public void apply(Register r) {<a name="line.39"></a>
<FONT color="green">040</FONT>                    if (target &gt;= r.getNumQbits() || target &lt; -1){<a name="line.40"></a>
<FONT color="green">041</FONT>                            throw new IllegalArgumentException("Target qubit not in register. Register size (qubits): " + r.getNumQbits() + " Target qubit: " + target);<a name="line.41"></a>
<FONT color="green">042</FONT>                    }<a name="line.42"></a>
<FONT color="green">043</FONT>    <a name="line.43"></a>
<FONT color="green">044</FONT>                    //phase shifting whole reg<a name="line.44"></a>
<FONT color="green">045</FONT>                    if (target==-1){<a name="line.45"></a>
<FONT color="green">046</FONT>                            gate = Z;<a name="line.46"></a>
<FONT color="green">047</FONT>                            for (int i=1;i&lt;r.getNumQbits();i++){<a name="line.47"></a>
<FONT color="green">048</FONT>                                    gate = gate.tensorProduct(Z);<a name="line.48"></a>
<FONT color="green">049</FONT>                            }<a name="line.49"></a>
<FONT color="green">050</FONT>                    }<a name="line.50"></a>
<FONT color="green">051</FONT>                    //case where target bit = 0<a name="line.51"></a>
<FONT color="green">052</FONT>                    else if (target==0){<a name="line.52"></a>
<FONT color="green">053</FONT>                            gate = Z;<a name="line.53"></a>
<FONT color="green">054</FONT>                            if (r.getNumQbits()&gt;1){<a name="line.54"></a>
<FONT color="green">055</FONT>                                    for (int i=1;i&lt;r.getNumQbits();i++){<a name="line.55"></a>
<FONT color="green">056</FONT>                                            gate = gate.tensorProduct(Matrix.IdentityMatrix(2));<a name="line.56"></a>
<FONT color="green">057</FONT>                                    }<a name="line.57"></a>
<FONT color="green">058</FONT>                            }<a name="line.58"></a>
<FONT color="green">059</FONT>                    }<a name="line.59"></a>
<FONT color="green">060</FONT>                    //all other cases<a name="line.60"></a>
<FONT color="green">061</FONT>                    else{<a name="line.61"></a>
<FONT color="green">062</FONT>                            gate=Matrix.IdentityMatrix(2);<a name="line.62"></a>
<FONT color="green">063</FONT>                            for (int i=1; i&lt;target; i++){<a name="line.63"></a>
<FONT color="green">064</FONT>                                    gate = gate.tensorProduct(Matrix.IdentityMatrix(2));<a name="line.64"></a>
<FONT color="green">065</FONT>                            }<a name="line.65"></a>
<FONT color="green">066</FONT>                            gate=gate.tensorProduct(Z);<a name="line.66"></a>
<FONT color="green">067</FONT>                            for (int i=target+1;i&lt;r.getNumQbits();i++){<a name="line.67"></a>
<FONT color="green">068</FONT>                                    gate = gate.tensorProduct(Matrix.IdentityMatrix(2));<a name="line.68"></a>
<FONT color="green">069</FONT>                            }<a name="line.69"></a>
<FONT color="green">070</FONT>                    }<a name="line.70"></a>
<FONT color="green">071</FONT>                    <a name="line.71"></a>
<FONT color="green">072</FONT>                    //now apply gate to register<a name="line.72"></a>
<FONT color="green">073</FONT>                    Matrix r_updated = gate.multiplyMatrix(r);<a name="line.73"></a>
<FONT color="green">074</FONT>                    r.update(r_updated);<a name="line.74"></a>
<FONT color="green">075</FONT>                    //normalise reg<a name="line.75"></a>
<FONT color="green">076</FONT>                    r.normalise();<a name="line.76"></a>
<FONT color="green">077</FONT>            }<a name="line.77"></a>
<FONT color="green">078</FONT>    <a name="line.78"></a>
<FONT color="green">079</FONT>            /**<a name="line.79"></a>
<FONT color="green">080</FONT>             * Returns the name of the gate regardless of representation.<a name="line.80"></a>
<FONT color="green">081</FONT>             */<a name="line.81"></a>
<FONT color="green">082</FONT>            public String getName() {<a name="line.82"></a>
<FONT color="green">083</FONT>                    return "Z Pauli";<a name="line.83"></a>
<FONT color="green">084</FONT>            }<a name="line.84"></a>
<FONT color="green">085</FONT>            <a name="line.85"></a>
<FONT color="green">086</FONT>    }<a name="line.86"></a>




























































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